Pigtail thread guide



NOV. 18,1947. 3, TAYLOR 2,431,150

PIGTAIL THREAD GI JIDE Filed Feb 24, 1945 Inventor: George F. Taylor,

y His zttor-ney.

Patented Nov. 18, 1947 PIGTAIL THREAD GUIDE George F. Taylor, Grosse Pointe Woods, Mich, assignor to Carboloy Company, Inc., Detroit, Mich, a corporation of New York Application February 24, 1945. Serial No. 519,600

11 Claims.

1 The present invention is a pigtail thread guide and more particularly a cemented carbide thread guide. Cemented carbides are well known and, in general, consist of sintered mixtures of one or the tube has been extruded and while it is still in a plastic condition it may be bent into the desired shape and then dried and thereafter sintered into a hard, dense mass. If desired, howmore hard metal carbides and a lower melting ever, after extrusion, the tube may be dried and point metal such as cobalt. Heretofore pigtail thread guides have been made from solid round steel rods or bars, also attempts have been made to employ solid cemented carbide pigtail guides as disclosed in McKenna Patent 2,220,018. In the prior steel guides as well as in the cemented carbide guide disclosed in the McKenna patent, the guide'is in contact with the thread at points along the circumference of a circle. In accordance with my invention the portion of the guide in contact with the thread is a substantially flat portion of a hollow cemented carbide tube. The tube originally is round in cross section but when bent to form a single turn of a spiral the bent portion of the tube assumes an elliptical shape in cross section and the thread comes in contact with the guide on a tangent parallel to the major axis of the ellipse.

One of the objects of the present invention is the provision of a cemented carbide thread guide requiring a minimum amount of metal. A further object of the invention is the provision of a thread guide which is wear resistant and which has a somewhat flat surface rather than a line in contact with the thread. Another object of the invention is the provision of a thread guide in which the thread may be readily inserted in the guide from either side thereof. Other objects will appear hereinafter.

The novel features which are characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, will best be understood from reference to the following specification when considered in connection with the accompanying drawing in which Fig. 1 is a plan view on an enlarged scale of my improved extruded cemented carbide thread guide; Fig. 2 is an end view partly in section of the thread guide illustrated in Fig. 1; Fi 3 is a view in cross section on a still further enlarged scale, on line 3-3 of Fig. 1; Fig. 4 is a plan view, on a greatly enlarged scale, of an extruded tube prior to bending it into the form of a thread guide; while Fig. 5 is an end view of the same.

In carrying out my invention, a cemented carbide mixture is extruded in tubular form as indicated at I in Fig. 4 of the drawing. This may be accomplished by the process disclosed in my prior Patent 2,271,960, February 3, 1942. After sintered into a hard, dense mass and thereafter heated to an elevated temperature and bent into the desired spiral 2 on a mandrel having a spiral groove thereon as set forth in my copending application, Serial No. 611,634, filed November 24,

1943, now Patent No. 2,422,636, dated June 17, 1947, and assigned to the same assignee as the present application.

The cemented carbide tube I employed as a thread guide in general is about two inches long having an outside diameter of about .1" and an inside diameter of about .06". When a cemented carbide tube having these dimensions is bent into a single convolution of spiral having an inside diameter of about 5 the free end portions 3 of the tube may be slightly curved as indicated in Fig. 1 or form substantially straight line extensions of circular cross sectional area.

The bent portions 4 of the tube I with which the thread comes in contact as it passes through the spiral assumes an elliptical cross section when bent, as clearly indicated in Fig. 3 of the drawing and the thread comes in contact with the inner, somewhat flat portion 6 of the ellipse. The

ratio of surface area of the ellipse presented to the thread to quantity of metal employed can be varied between wide limits by varying the wall thickness of the tube, the thinner the wall the more elliptical the tube will be when bent into'a circle or spiral and the less metal it will contain.

Also, if it is desired to employ a spiral tube which has a greater elliptical surface, the tube may be extruded in the form of a tube having an elliptical cross section. This extrusion may be accomplished by the use of an elliptical extrusion die l My improved thread guide not only requires a minimum of metal in its manufacture but is also resistant to wear and easier to manufacture than a solid rod. For example, a cemented carbide solid rod bent into a radius as small as that employed in the thread guide hereinbetore disclosed will very likelybreak particularly if the quantity of cobalt employed in the cemented so/carbide is not very high. A thread guide however preferabl should be made of the hardest and most wear resistant grades of carbide which are those having the lowest cobalt content, for

- example about 1 to 6% cobalt. A cemented carbid elliptical tube containing that amount of .3 cobalt can be bent easily into a circle or spiral of small radius whereas it is extremely doubtful that a solid rod of the same composition and diameter could be bent into a circle of the same diameter without breaking. The reason for this resides in the fact that when a tube is bent the deformation is largely in a radial direction which results in flattening the tube and giving it an elliptical cross section whereas in the case of a solid red the deformation is linear and of greatest extent on the outside of the circle. For this reason a cemented carbide tube can be bent into a circle of smaller radius than a solid rod of the same diameter, other things being equal.

The bent spiral thread guide as disclosed in Fig. 2 of the drawing, is brazed or soldered to a metal supporting rod 6. The extensions 8 forming the free end portions of the thread guide extend an appreciable distance beyond its circular portion and act as hooks thereby making it easy for the operator to engage the thread into the circular portion of the guide and from either side thereof. The angle formed by each free end portion 8 with the metal support 6 is less than 90 but more than 45.

The cemented carbide thread guide has several advantages over the solid. guide, one of which is the saving of material since obviously less material is required to make a tube than would be required to make a solid pigtailof the same diameter. Moreover, by employing a plgtail guide which has a bearing surface consisting of the portion of an ellipse opposite its major axis, the life of the guide is increased since the surface presented to the thread is greater than is the case with a round rod of the same diameter and having a circular cross section.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A thread guide comprising a cemented carbide tube bent into the form of a spiral.

2. A thread guide comprising a cemented carbide tube bent into the form of a spiral having free end portions, each of said end portions extending well beyond said spiral.

3. A thread guide comprising a cemented carbide tube bent in the form of a single convolution of a spiral to thereby provide an elliptical contact surface for the thread, the bearing surface being in the direction of the major axis of the ellipse.

d. A thread guide having a spiral portion conslsting of a hollow cemented carbide tube.

5. A hollow cemented carbide thread guide bent into the form of a spiral, the bent portion of said guide being elliptical in cross section.

6. A thread guide bent in the form of a spiral having free end portions which extend beyond said spiral and on either side thereof, said end portions serving as hooks to facilitate engaging the thread with said spiral, said spiral being secured at approximately its mid-point to a metal support.

7. A pigtail thread guide consisting-of a cemented carbide tubular portion bent into the form of a single convolution of a spiral and secured at its mid-point to a metal support.

8. A pigtail thread guide consisting of a cemented carbide tubular portion bent into the form of a single convolution of a spiral and secured at its mid-point to a metal support, the free end portions of said spiral forming an angle of less than but more than 45 with said metal support.

9. A pigtail thread guide consisting of a cemented carbide tubular portion bent into the form of a single convolution of a spiral and secured at approximately its mid-point to a supporting member, each of the free end portions of said spiral extending in a substantially straight line beyond said spiral and forming an angle of less than 90 but more than 45 with said supporting member.

10. A cemented carbide thread guide bent into the form of a spiral, the bent portion of said guide being elliptical in cross section.

11. A cemented carbide thread guide bent into the form of a spiral, the bent portion or said guide being elliptical in cross section, said spiral having free end portions each of which said end portions extending well beyond said spiral.

GEORGE F. TAYLOR.

REFERENCES CITED The following references are of record in the tile of this patent: 

